Re: [PATCH] hpsa: do not attempt to read from a write-only register [LWN.net]

From:		Andrew Morton <akpm-AT-linux-foundation.org>
To:		"Stephen M. Cameron" <scameron-AT-beardog.cce.hp.com>
Subject:		Re: [PATCH] hpsa: do not attempt to read from a write-only register
Date:		Mon, 11 Jul 2011 13:19:11 -0700
Message-ID:		<20110711131911.31789ee0.akpm@linux-foundation.org>
Cc:		james.bottomley-AT-hansenpartnership.com, linux-scsi-AT-vger.kernel.org, linux-kernel-AT-vger.kernel.org, stephenmcameron-AT-gmail.com, thenzl-AT-redhat.com, mikem-AT-beardog.cce.hp.com
Archive-link:		Article, Thread

On Fri, 08 Jul 2011 14:59:26 -0500
"Stephen M. Cameron" <scameron@beardog.cce.hp.com> wrote:

> From: Stephen M. Cameron <scameron@beardog.cce.hp.com>
> 
> Most smartarrays tolerate it, but a few new ones don't.
> 
> Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
> ---
>  drivers/scsi/hpsa.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/hpsa.h b/drivers/scsi/hpsa.h
> index 6d8dcd4..7f53cea 100644
> --- a/drivers/scsi/hpsa.h
> +++ b/drivers/scsi/hpsa.h
> @@ -214,7 +214,7 @@ static void SA5_submit_command(struct ctlr_info *h,
>  	dev_dbg(&h->pdev->dev, "Sending %x, tag = %x\n", c->busaddr,
>  		c->Header.Tag.lower);
>  	writel(c->busaddr, h->vaddr + SA5_REQUEST_PORT_OFFSET);
> -	(void) readl(h->vaddr + SA5_REQUEST_PORT_OFFSET);
> +	(void) readl(h->vaddr + SA5_SCRATCHPAD_OFFSET);
>  	h->commands_outstanding++;
>  	if (h->commands_outstanding > h->max_outstanding)
>  		h->max_outstanding = h->commands_outstanding;

The changelog forgot to tell us the user-visible effects of the bug. 
That was really really bad of it.  Bad changelog.  No bone for you.

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